In many instances, it is desirable to capture images where there are both very bright and very dark areas within the field of view. If a short capture interval is used, details within the bright areas can be imaged successfully but the darker areas remain unclear. If a longer capture interval is used, details within the darker areas can be imaged successfully but the brighter areas are saturated.
To overcome these issues, it is known to combine images captured using different capture intervals to produce a composite image having detail in both the light and dark areas. Commonly, two different capture intervals are used. In a particular method, two capture intervals are alternated frame by frame. Typically, the imaging array may operate in an interlaced manner such that the alternate images are captured using alternate rows of detector pixels within the array. In a similar manner, the resultant output can be interlaced. This provides a simple way of implementing this process. Additionally, for a steady scene, pixels in the output frames consistently map to detector elements operating at the same capture interval, providing a steady output image.
In the event that the dynamic range of any such images is insufficient, it is possible to use more than two capture intervals. This however causes a number of difficulties. Where three capture intervals are used, in a simple sequence, then interlacing is problematic. This is because the pixels in successive output frames at a given capture interval map on to alternate rows of detector elements. Hence for a steady scene, the output frames appear to ‘bounce’ by one line.
An additional difficulty with acquiring successive images at the different capture intervals and using these groups of successive images to generate a composite image is that this does reduce the effective frame rate. This is a particular problem with standard capture electronics as these operate at a fixed refresh rate (typically 50 Hz or 60 HZ). Accordingly, even where short capture intervals are used, each successive capture interval starts 20 ms (50 Hz systems) or 16.7 ms (60 Hz systems) after the previous capture interval. In many cases combining groups of successive images to generate a composite image can reduce the effective frame rate sufficiently that the human eye no longer perceives the output as smooth.
It is therefore an object of the present invention to provide a new method and system for high dynamic range imaging that at least partially overcomes or alleviates the above problems.